For preparation of 3,5-difluoroaniline there have been known the method described in Finger et al, J. Am. Chem. Soc., 73, 153 (1951), wherein 3,5-difluoroaniline is prepared from 2,4-difluoroaniline as a starting material through five reaction steps; and Ishikawa et al, Nihon Kagaku Zasshi, 87, 1089 (1966) and ibid 86, 1202 (1965), wherein 1,3,5-trichloro-2,4,6-trifluorobenzene is used as a starting material.
The former method, however, involves many reaction steps for synthesis of the starting material 2,4-difluoroaniline, and produce the final product only in a low yield. 1,3,5-Trichloro-2,4,6-trifluorobenzene used in the latter method as a starting material is prepared from hexachlorobenzene, which has been designated as a specific chemical substance of the first type under "Law Concerning the Examination and Regulation of Manufacture, Etc. of Chemical Substances" in Japan, so that hexachlorobenzene is not readily available and handling of the compound involves various problems.
2-Chloro-3,5-difluoroaniline has been known to be produced by substituting an amino group of 2,4-difluoro-6-nitroaniline with a chlorine atom and then converting the nitro group into an amino group, as described in Finger et al, J. Fluorine Chem., 1, 415-425 (1971/1972). In more detail, the process comprises subjecting 2,4-difluoroaniline to acetylation and nitration (according to the method as described in Finger et al, J. Amer. Chem. Soc., 73, 153 (1951)) to synthesize 2,4-difluoro-6-nitroaniline, followed by diazotization of the amino group of the compound in the presence of cuprous chloride (Sandmeyer reaction), and then reducing the resulting 2-chloro-3,5-difluoronitrobenzene to obtain 2-chloro-3,5-difluoroaniline. This process involves many reaction steps and provides the final product only in a low yield.